Spam complaint rate
Spam complaint rate is the share of delivered emails that recipients mark as spam, and Gmail wants it to stay below 0.3 percent.
When a person clicks 'Report spam', the provider counts it as a complaint. The complaint rate is complaints divided by delivered messages. It is the strongest negative signal you can send to a provider, much stronger than a bounce.
Gmail and Yahoo set clear limits for bulk senders: keep the rate below 0.3 percent, and Google advises to stay well under 0.1 percent. Gmail shows your rate in Google Postmaster Tools. Not every provider shares complaint data with senders, so your own numbers are often a lower bound.
In cold email, complaints come from poor targeting, a message that hides who you are, no easy way to opt out, and too many follow-ups. A clear opt-out is better than a complaint. To lower the rate: send only to people who have a real reason to hear from you, state who you are in the first lines, add a simple unsubscribe option, and stop the sequence when someone says no.
In Terlido
Terlido pauses a campaign when it recorded a spam complaint for that campaign in the last 24 hours, whatever the send volume is.